In recent years, magnetic recording devices such as a magnetic disc device, a flexible disc device, and a magnetic tape device have been used over a remarkably wide and increasing range of applications, and have grown in importance. Along with this, attempts continue to be made to greatly increase the recording density of the magnetic recording medium for use in such recording devices. In particular, an areal density has been intensively increased since the introduction of an MR head and a PRML technology. Moreover, a GMR head and a TMR head or the like have also been introduced recently, and the areal density keeps increasing at a rate as high as about 100% per year.
There is a demand for such a magnetic recording medium to have a higher recording density in the future. It is therefore necessary to increase a coercive force, a signal-to-noise ratio (SNR), and a resolution of the magnetic layer. Recently, efforts to increase the areal density by increasing both a track density and a linear recording density have been made.
The up-to-date magnetic recording device has a track density as high as 110 kTPI. As the track density increases, however, magnetic recording information between adjacent tracks begins interfering with each other. As a result, a magnetizing transition area of the border area thereof becomes a noise source, which may easily adversely affect the SNR. The decrease of the SNR may directly lead to a decrease in a bit error rate and hinder improvement in the recording density.
In order to increase the areal density, it is necessary to make the size of each recording bit on the magnetic recording medium finer and to ensure that a saturation magnetization and a magnetic film thickness be as large as possible for each recording bit. However, as the recording bits become finer, the magnetization minimum volume per single bit becomes smaller, and the recorded data may disappear due to magnetization reversal caused by heat fluctuation.
Since the adjacent tracks come close to each other as the track density increases, a very highly precise track servo technique is necessary for the magnetic recording device. In addition, in the generally used method, recording is performed in a wide range, and reproducing is narrowly performed in order to eliminate possible influence from adjacent tracks. However, although the influence between the tracks can be suppressed to the minimum by this method, it is difficult to obtain a sufficient reproduction output, and as a result it is difficult to ensure a sufficient SNR.
As one way to address such a heat fluctuation problem, to achieve a sufficient output, and to ensure the SNR, there has been an attempt to increase the track density by forming unevenness along the track on the surface of the recording medium and physically separating recording tracks. Such a technique is usually called a discrete track method, and a magnetic recording medium manufactured thereby is called a discrete track medium. An attempt has also been made to produce a so-called “patterned medium” by further dividing data areas in the same track.
As an exemplary discrete track medium, a magnetic recording medium is known, in which the magnetic recording medium is formed on the non-magnetic substrate which has an uneven pattern on the surface, and a physically separated magnetic recording track and a servo signal pattern are formed (for example, refer to Japanese Unexamined Patent Application, No. 2004-164692).
In the disclosed magnetic recording medium, a ferromagnetic layer is formed through a soft magnetic layer on the substrate surface with a plurality of projections and recesses thereon, and a protective film is formed thereon. In this magnetic recording medium, a magnetic recording region physically separated from the surroundings is formed in a projection area.
According to the disclosed magnetic recording medium, generation of a magnetic wall on the soft magnetic layer can be suppressed, the influence of the heat fluctuation can thus be made difficult, and no interference occurs between adjacent signals. As a result, it is possible to form a high-density magnetic recording medium with little noise.